As it is known, many food products, such as fruit juice, pasteurized or UHT (ultra-high-temperature treated) milk, wine, tomato sauce, etc., are sold in packages made of sterilized packaging material.
A typical example of this type of package is the parallelepiped-shaped package for liquid or pourable food products known as Tetra Brik Aseptic (registered trademark), which is made by folding and sealing laminated strip packaging material.
The packaging material has a multilayer structure substantially comprising a base layer for stiffness and strength, which may be defined by a layer of fibrous material, e.g. paper, or mineral-filled polypropylene material; and a number of layers of heat-seal plastic material, e.g. polyethylene film, covering both sides of the base layer.
In the case of aseptic packages for long-storage products, such as UHT milk, the packaging material also comprises a layer of gas- and light-barrier material, e.g. aluminium foil or ethyl vinyl alcohol (EVOH) film, which is superimposed on a layer of heat-seal plastic material, and is in turn covered with another layer of heat-seal plastic material forming the inner face of the package eventually contacting the food product.
As is known, packages of this sort are produced on fully automatic packaging machines, on which the tube is formed continuously from the web-fed packaging material. More specifically, the web of packaging material is unwound off a reel and fed through a station for applying a sealing strip of heat-seal plastic material, and through an aseptic chamber on the packaging machine, where it is sterilized, e.g. by applying a sterilizing agent such as hydrogen peroxide, which is subsequently evaporated by heating, and/or by subjecting the packaging material to radiation of appropriate wavelength and intensity.
The web of packaging material is then fed through a number of forming assemblies which interact with the packaging material to fold it gradually from strip form into a tube shape.
More specifically, a first portion of the sealing strip is applied to a first longitudinal edge of the packaging material, on the face of the material eventually forming the inside of the packages; and a second portion of the sealing strip projects from the first longitudinal edge.
The forming assemblies are arranged in succession, and comprise respective roller folding members defining a number of packaging material passages varying gradually in cross-section from a C shape to a substantially circular shape.
On interacting with the folding members, the second longitudinal edge is laid on the outside of the first longitudinal edge with respect to the axis of the tube being formed. More specifically, the sealing strip is located entirely inside the tube, and the face of the second longitudinal edge facing the axis of the tube is superimposed partly on the second portion of the sealing strip, and partly on the face of the first longitudinal edge located on the opposite side to the first portion of the sealing strip.
Packaging machines of the above type are known in which the first and second longitudinal edges are heat sealed within the aseptic chamber to form a longitudinal seal along the tube, which is then filled with the sterilized or pasteurized food product.
Furthermore, packaging machines of the above type comprise a forming unit in which the tube and is sealed and cut along equally spaced cross sections to form pillow packs.
Forming unit comprise two or more jaws which cyclically interact with the tube to seal it.
Pillow packs are then folded mechanically to form respective packages at a folding unit, which is arranged downstream from the movable components of the forming unit.
In detail, the forming unit is arranged downstream from the aseptic chamber, with reference to the advancing direction of the tube.
Furthermore, a seal separates in a tight-fluid way the aseptic chamber from the forming unit, by exerting a pressure against the tube of packaging material.
However, some residues of peroxide inevitably pass through the seal, especially when the web of packaging material is provided with a plurality of closable opening devices which are applied by injecting plastic material directly onto the web.
As a matter of fact, the opening devices advancing with the tube move away the seal from the outer diameter of the tube, so reducing the effectiveness of the seal in tight-fluid separating the aseptic chamber.
This situation is exacerbated by the fact that the high speed at which the tube is fed renders the lapse of time between the passages of two subsequent opening devices against the seal very short. Accordingly, the lapse of time during which the seal effectively presses against the tube is reduced.
The peroxide residues may penalize the wear resistance of mechanical components of the forming and folding units, for example the jaws.
Accordingly, a need is felt within the industry to reduce as far as possible the amount of peroxide which may pass through the seal and possibly contact the forming unit or other downstream components of the packaging machines.
Furthermore, the forming unit is normally accessible by a human operator.
European regulations require that peroxide residues in the air be under a certain threshold at the stations of the packaging machine which are accessible from the human operator, for example the forming and folding units.
A need is felt, therefore, to reduce as far as possible the peroxide concentrations in those stations of the packaging machines which are accessible by the human operator and are arranged downstream from the seal.